1. Field of the Invention
The present invention relates to a dispersed solution of carbon nanotubes and a method of preparing the same. More particularly, the present invention relates to a dispersed solution of carbon nanotubes including a spacer and a dispersant, and a method of preparing the same.
2. Description of the Related Art
Since discovery of carbon nanotubes (CNTs) by Iijima in 1991, carbon nanotubes have attracted tremendous research interests as new materials. Carbon nanotubes are tubes made of carbon atoms arranged in a hexagonal, honeycomb-like structure, and have new physical properties due to their nanometer-scale diameters.
The electrical characteristics of carbon nanotubes depend on the structure and diameter of the carbon nanotubes. That is, carbon nanotubes can behave like insulators, semiconductors, or conductors according to their structure and diameter. For example, if the shape or chirality of insulating, spiral carbon nanotubes is changed, motion of free electrons in the carbon nanotubes is changed. As a result, the carbon nanotubes behave like conductors due to relatively free motion of the free electrons or semiconductors due to the presence of barriers.
Carbon nanotubes have characteristics of good dynamic robustness and chemical stability, of both semiconductors and conductors, and of a small diameter, a long length, and a hollow center. Thus, carbon nanotubes are suitable as materials for use in flat panel displays, transistors, energy storage media, and the like, and have high applicability to various nanometer-scale electronic devices.
In order for carbon nanotubes to be used in formation of conductive films or in manufacturing of various electronic devices, the carbon nanotubes must be effectively dispersed in a matrix such as a solution or a polymer. However, carbon nanotubes tend to agglomerate into bundles in a matrix due to a strong van der Waals forces. Thus, carbon nanotubes are hardly soluble in water or other solvents, which makes it difficult to process the carbon nanotubes.
If carbon nanotubes agglomerate in a matrix, the intrinsic characteristics of the carbon nanotubes may be degraded, or upon formation of a thin film, uniformity of the film's thickness may decrease.
Due to the unique properties of carbon nanotubes, only use of commercially available dispersants makes it difficult to obtain a dispersed solution of carbon nanotubes which are sufficiently dispersed. Thus, various dispersion methods such as use of a new dispersant for uniformly dispersing or solubilizing carbon nanotubes in a solution or a binder have been proposed.
One method includes incorporating an alkyl group to carbon nanotubes using a chemical bond, another includes increasing the solubility of carbon nanotubes by surrounding the carbon nanotubes with a polymer capable of physically interacting with the carbon nanotubes, and another method includes attaching to carbon nanotubes at least one functional group selected from the group consisting of a cyano group, an amino group, a hydroxyl group, a carboxyl group, a halide group, a nitrate group, a thiocyano group, a thiosulfuric acid group, and a vinyl group. Although these methods can partially improve the dispersibility of carbon nanotubes, a cost increase may be incurred and the physical properties of the carbon nanotubes may be altered due to surface modification.
One method of improving the dispersibility of carbon nanotubes includes fluorinating the surfaces of the carbon nanotubes, another method includes sonicating a carbon nanotube-containing solution, and another includes using an aromatic polyamide as a dispersant. According to the above technologies, however, bundled carbon nanotubes are incompletely separated, which restricts the dispersion of carbon nanotubes.
In view of the above problems, there remains a need to develop a method of improving the dispersibility of carbon nanotubes.